Band 91, Heft 3-4 - Special Issue: Sensoren in Faser-Kunststoffverbunden/ Sensors in fiber-plastic composites; Guest Editors: Johannes Mersch, Gerald Gerlach and Paul Motzki

Bird strikes on wind turbine rotor blades have long-term impacts on fibre reinforced plastic composites. To monitor and document these impacts, integrating sensors into the composite structure is necessary. However, conventional sensors introduce foreign objects that deflect the fibre orientation, weakening the composite and potentially causing damage like delamination. To address this, silver-coated glass fibre sensors have been developed and integrated into the composite structure. Impact tests confirmed the functionality of the developed sensors. These sensors seamlessly integrate into the reinforcing structure due to their textile nature and multi-layered fibre structure. Unlike conventional sensors, they do not introduce foreign objects or create mechanical weak spots. Instead, they are expected to contribute to the overall stability of the component. In summary, integrating impact sensors into fibre reinforced plastic composites is crucial for documenting bird strike damage. Conventional sensors weaken the composite, but silver-coated glass fibre sensors resolve this issue by seamlessly integrating into the structure, enhancing stability and durability.

This research addresses the challenging task of monitoring the structural integrity of fiber-reinforced composite (FRC) components under complex loading conditions. Ensuring the safety and functionality of these components is critical but economically challenging. Therefore, this study presents an innovative approach using textile-based strain sensors that are cost-effective and structurally compatible with carbon fiber-reinforced plastic (CFRP) components. The investigation includes the systematic electromechanical characterization and comparison of four different sensor materials at the yarn and composite scale in various test scenarios. Cyclic tensile, compression, and bending tests of CFRP specimens are performed and show good reproducibility of sensor signals within the elastic range, with significant agreement observed with applied strain measurement methods, particularly in tensile tests. Although there are minor deviations in compression and bending evaluations, the signals are still meaningful for in-situ detection of complex loading patterns, crack initiation, and structural failure. The study demonstrates that the integration of textile-based sensor yarns allows for continuous structural health monitoring (SHM) of CFRP components under various loading scenarios, including tensile, bending, and especially compressive loads.

In this paper, we present a comprehensive overview of our research in the field of distributed fiber optic sensors for structural health monitoring of hydrogen composite pressure vessels. Specifically, we demonstrate how the integration of fiber optic sensors into composite pressure vessels enhances safety while simultaneously reducing maintenance costs. The small size of optical fibers enables their integration into composite structures during the manufacturing process, allowing continuous monitoring and precise detection and localization of structural damages during service life. We also discuss the potential of state-of-the-art signal processing methods and machine learning for advancing predictive maintenance. Our applications of fiber optic sensors demonstrate their potential to contribute significantly to the energy transition towards renewable sources.

Strain sensors for fiber-reinforced plastics require higher elasticity and fatigue resistance than conventional strain gauges. Elastic strain sensors made of shape-memory alloys (SMA) meet this requirement. Due to greater elasticity, other procedures are required for their calibration than those recommended in standards. This paper presents a calibration method for shape-memory strain sensors as a function of ambient temperature and methods for temperature compensation are investigated. SMA strain sensors are manufactured as sensor patches from wire and layers of glass fiber fleece infiltrated with epoxy resin. The patches are bonded to bending specimens made of glass-fiber plastic composites. The calibration of the SMA sensors is implemented by means of a 4-point bending test using a self-built test stand. This is designed for operation in a climate chamber. The results show successful proof of feasibility of temperature compensation. The variation of the sensor signal in the unloaded state in the temperature response is less than 0.4 mV/V. The gauge factor depends on the temperature and is compensated by means of a regression with temperature sensor data. In combination with a temperature sensor, an almost complete compensation of the temperature-dependent behaviour is possible. A procedure is realised for calibrating SMA sensors at larger strains.

Due to recent progress in human-machine interaction the development of interfaces ensuring a safe collaboration between handling devices and workers is gaining in importance and impact to the industry field. For an adequate operation, combined sensing and actuation capabilities are sufficient for interaction units. Smart materials like dielectric elastomers (DEs) are predestinated for integrated multi-functional applications. DEs are lightweight, high energy density and highly stretchable transducers suitable for many different operation areas, like movement tracking, force sensing, haptic feedback and sound generation and can be used to develop highly integrated textile-based user interfaces. This paper shows first results on the development of a novel intelligent glove prototype based on DE elements. The main focus of this investigation lies on DE-based integrated joint angle and force measurement units as well on a cost-efficient and slim sensing electronic. By embedding the resulting system in an Industry 4.0 environment, an adaptive assistance tool can be developed. The resulting system can be used to monitor the desired motion of a worker and to respond with a corresponding haptic feedback, which depends on the specific interaction task. This makes the resulting system a novel, portable assistant tool for industrial environments.

This paper presents a measurement setup which is able to measure the distribution of small scale pressure on an area of 15.2 mm × 30.4 mm with a sample rate up to 1.2 kHz. It was used to investigate the contact pressures of vocal folds during phonation. This was performed in ex vivo experiments of 11 porcine larynges. The contact pressure at the medial surface and other phonation parameters, as the glottal resistance and the closing velocity of the vocal fold, were measured at different adduction and elongation levels and air flow rates. A statistical analysis was carried out. It could be shown that the contact pressure rises, when the vocal fold is manipulated or when the flow rate is increased.

The combination of flexibility and high integrability as well as their precise sensing capability enable dielectric elastomer sensors to be integrated into a variety of applications. Because of these integration opportunities especially in the field of smart textiles these sensor systems can make a difference. Sensor inlays for shoes based on resistive and capacitive sensors enable a partial monitoring of the loads and load distributions on our feet while the interaction with the shoe shaft remains unknown. The novel sensor integration into the shaft combined with a wireless real-time measurement is being studied in this work. This new sensor system within the shoe creates the basis for the data acquisition to finally support diabetic patients who suffer under the diabetic foot syndrome, to support athletes analyzing walking patterns as well as bringing safety shoes to a digital age. This contribution displays sensor concepts as well as the corresponding electronics development. The first smart shoe concentrates on the integration of six shaft sensors distributed over the shoe and their measurement in real-time. The shoe is designed and manufactured in collaboration with the Prüf- und Forschungsinstitut Pirmasens. The evaluation of the sensor signals allows the analysis of different load scenarios.